Plasma source assembly and method of manufacture

ABSTRACT

A plasma source assembly including an outer shield, a dielectric chamber wall, and a helical coil provided between the outer shield and the dielectric chamber wall. The plasma source assembly also includes a coil support assembly configured to facilitate repeatable performance of the helical coil. Preferably, the assembly includes a plenum cooling plate that is configured to supply cooling fluid to a first cooling rod provided within a resonator cavity defined by the chamber wall and the outer shield, and receive cooling fluid from a second cooling rod provided within the resonator cavity. The assembly preferably also includes a spacer provided between the first cooling rod and the second cooling rod, and coil insulators having holes configured to receive the helical coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/601,590, filed Jun. 24, 2003, which is a non-provisionalapplication claiming priority under 35 USC § 119(e) of U.S. ApplicationNo. 60/390,361, filed on Jun. 24, 2002. This application is related toU.S. Application Nos. 60/291,337, filed May 17, 2001 and 09/774,182,filed on Feb. 5, 2001, now U.S. Pat. No. 6,491,742, issued Dec. 10,2002. The entire contents of each of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to manufacturing of semiconductorintegrated circuits.

2. Discussion of the Background

Manufacturers of semiconductor integrated circuits are faced withintense competitive pressure to improve their products and processesused to fabricate the products. The manufacturers have a large businessmotivation to lower production costs by improving product throughput,quality and complexity. Additionally, manufacturers have a need forrepeatability and consistency in the assembly and functioning ofsemiconductor fabrication equipment. Accordingly, semiconductormanufacturers strive to formulate a low cost way to manufacture highquality process equipment.

One goal of semiconductor manufacturers is to improve tool performanceat a low cost. Another goal is to make process equipment function thesame regardless of particular hardware sampled. The company that canenhance tool performance without increasing tool cost is in a positionto increase profit margins. In cyclical industries such as thesemiconductor capital equipment industry, increased profit margins canhave a dramatic impact on market penetration.

For many years Inductively Coupled Plasma (ICP) sources have been usedin a variety of applications. Most recently, low pressure (<100 mTorr)ICP sources have been used in wafer production where plasmas arerequired to deliver high densities of ions, electrons and radicals withhigh uniformity over wafer diameters of 200 mm and larger. These plasmasources need to deliver ions that are uniform in density and energydistribution while keeping ion and electron energy very low.

The Electrostatically Shielded Radio Frequency (ESRF) plasma source is atype of ICP source which is particularly useful in applications wheresubstrate materials are susceptible to damage from high energy plasmaions or electrons, uncontrolled bias voltages and thermal fluxes. ESRFsources feature pure inductive coupling with reduced capacitivecoupling. The radio frequency (RF) power produces only plasma densityand induces very little voltage on the plasma. This inductive couplingis sufficiently devoid of capacitive coupling so that the plasma doesnot search for counter electrodes. The plasma remains mainly within theprocess (dielectric) chamber at all powers and pressures.

The main components of an ESRF ICP processing system are depicted in thegeneric FIG. 1. The ESRF ICP processing system 10 includes a processchamber 20 with a wafer and chuck assembly 30 provided therein. A gasinject assembly 40 is provided opposite the wafer and chuck assembly 30.A plasma region or area 22 is provided adjacent a dielectric chamberwall 60 in between the wafer and chuck assembly 30 and the gas injectassembly 40.

The plasma source is composed of several main elements and is affixed toan opening of a suitable process chamber 20. A wafer that is beingprocessed is located on the chuck assembly 30. The plasma sourcecomprises a resonator chamber or cavity 72 bounded by an outer shield orhousing 50 and the dielectric chamber wall 60, within which a helicalcoil 90 is mounted. The outer shield 50 and the dielectric chamber wall60 further define a fluid cooling area 70, within which the helical coil90 is immersed. The dielectric chamber wall 60 contains the plasma area22 of the plasma source. Furthermore, the dielectric chamber wall 60 hasappropriate sealing devices to seal cooling fluid within fluid coolingarea 70 and maintain the process pressure within plasma area 22 atappropriate levels. Additionally, an electrostatic shield 80 is providedon an outer surface of the dielectric chamber wall 60 in an interior ofthe fluid cooling area 70.

In the construction of ESRF source assemblies, there are severalelements that are expensive to fabricate for various reasons. The outershield or housing can be the most expensive part in the source. It canbe fabricated from several aluminum parts and subsequently furnace ordip brazed to form a singular assembly. The interface of these partsmust be machined to tolerances required in the brazing process. Oncemachined, the parts are then assembled utilizing an appropriate holdingfixture and brazed using the specified processes. Various machiningoperations must then be performed on the resulting brazed assemblybefore it is ready for use.

Another problem seen in ESRF plasma sources is the method andrepeatability of mounting the helical coil. In ESRF plasma sources,particularly those sources comprising a quarter-wave or half-waveresonant coil, the coil is tuned to a particular frequency. In order totune the helical coil to a particular frequency, a labor intensiveprocess of adjusting the length of the coil is involved. Once the coilis tuned, changes in coil position can adversely affect the tuning.

SUMMARY OF THE INVENTION

The present invention advantageously provides a plasma source assemblyincluding an outer shield, a dielectric chamber wall, and a helicalcoil. The helical coil is advantageously mounted within a cavity boundedby the outer shield and the dielectric chamber wall.

It is an object of the invention to produce the outer shield (housing)in a very cost effective manner that requires no special processes ormachining after original fabrication of the parts. Such a sourceassembly configuration may allow quick changes and modifications to theouter shield housing and electrostatic shield using many original parts,without other special processes or special tools.

In the preferred embodiment of the present invention, the plasma sourceassembly further includes an electrostatic shield provided outside thedielectric chamber wall, forming an interior of the cavity. The plasmasource assembly preferably includes a plenum cooling plate defining amanifold configured to supply cooling fluid to the cavity and a gasinject assembly attachable to the outer shield.

The plasma source assembly preferably includes structure for stackingand detachably joining a plurality of plates to form the outer shield,and structure for constructing the gas inject assembly and thedielectric chamber wall to be removable from the plasma source assemblywithout using a tool. The preferred embodiment of the present inventionincludes structure for circulating cooling fluid throughout the cavityand the gas inject assembly, and structure for removing bubbles from thecooling fluid within the cavity.

It is another object of the present invention to provide a coil supportassembly and method that supports, separates, and holds the helical coilin such manner that the plasma source only needs to be tuned once. Sucha manufacturing method makes helical coil tuning repeatable even aftercomplete disassembly and subsequent reassembly of the entire plasmasource assembly.

It is a further object to circulate cooling fluid throughout the plasmasource and the gas inject assembly in a way that promotes efficientcooling, and also removes and discourages the forming of any bubbles inthe cooling fluid. Air bubbles, especially bubbles located inside theresonator cavity, degrade the insulating properties of the dielectriccooling fluid. Maintenance and cleaning are needed to ensure thatacceptable process conditions are met. One aspect of maintenance andcleaning is the removal of the dielectric chamber wall for wet cleaning.A goal of maintenance and cleaning operations is short machine downtime.Thus, preferably the dielectric chamber wall (process tube) may beremoved and the inject assembly may be removed and/or replaced formaintenance purposes quickly without using tools.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will become readily apparent with reference to thefollowing detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

FIG. 1 is a general section view of an electrostatically shielded radiofrequency (ESRF) inductively coupled plasma (ICP) source;

FIG. 2 is a section view of an ESRF ICP source according to the presentinvention;

FIG. 3 is a perspective view of an assembly including a helical coil,cooling rods, and spacers according to the present invention;

FIG. 4 is a side view of an assembly including a helical coil, coolingrods, and spacers according to the present invention; and

FIG. 5 is an exploded view of an assembly including a helical coil,cooling rods, and spacers according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a section view of an ESRF ICP source according to oneembodiment of the present invention. The present invention provides aninexpensive, dielectric fluid cooled, efficient, ESRF ICP plasma sourcethat can easily be modified, remains tuned to a particular frequency,and can easily and quickly be cleaned.

FIG. 2 depicts an ESRF ICP plasma source assembly 110 that generallyincludes a process chamber 120 with a wafer and chuck assembly 130provided therein. A gas inject assembly 140 is provided opposite thewafer and chuck assembly 130. A plasma region or area 122 is providedadjacent a dielectric chamber wall 160 in between the wafer and chuckassembly 130 and the gas inject assembly 140. An outer shield or housing150 is mounted between the process chamber 120 and the gas injectassembly 140. The outer shield 150 and the dielectric chamber wall 160define a resonator cavity 172 that bounds a fluid cooling area 170. Anelectrostatic shield 180 is provided outside the dielectric chamber wall160 forming an interior wall in the fluid cooling area 170. A coil 190is provided within the resonator cavity 172 of the fluid cooling area170.

FIG. 2 depicts a plasma source assembly 110 having a generally conicalinner surface. The configuration of the plasma source of the presentinvention is not restricted to a conical inner shape. For example, theplasma source assembly can be configured with a cylindrical, spherical,semi-spherical, or other shape inner surface.

In the embodiment depicted in FIG. 2, the outer shield or source housing150 is comprised of three separate manufactured plates 152, 154, 156.The plates of the housing 150 are made from aluminum plate stock,although other metallic materials or alloy materials can alternativelybe used. The plates of the housing 150 can be formed of variousthickness, depending upon source size and process requirements. Theplates 152, 154, 156 are machined in a manner that, when completed, theycan be stacked and detachably joined or fastened together with commonhardware 155 as shown. O-ring seals 158 are inserted during assembly toprevent leakage of dielectric cooling fluid. Grounding devices 159 arealso inserted between respective plates during assembly. The groundingdevices 159 ensure RF grounding requirements are met. The plates 152,154, 156 are also constructed in such a manner that cooling rod-mountingfeatures are provided where necessary. The cooling rod-mounting featurescan simply be through holes and/or blind counter bores as needed.

The embodiment depicted in FIG. 2 has three plates 152, 154, 156 thatform the outer shield or source housing 150. The present invention canbe constructed having an outer shield formed with one or two plates, orwith four or more plates depending upon individual plasma sourceconfiguration requirements. However, the plates of the outer shield ofthe present invention do not require brazing or post machining of partsin any of these configurations. In an alternative embodiment, the outershield or source housing 150 is formed from a rolled-ring forging asdescribed in pending U.S. Patent App. Ser. No. 60/291,337 (filed on May17, 2001).

The electrostatic shield 180 is attached to the inner diameters of theupper and lower plates of the source housing 150, thereby forming aninterior wall of the resonator cavity 172. The electrostatic shield 180has a number of slots positioned in a predetermined arrangement. Theelectrostatic shield 180 is attached to the cavity 172 using commonhardware. Grounding features can be utilized with the electrostaticshield 180 if desired. The electrostatic shield 180 is preferably madefrom aluminum alloy sheet stock, however alternative materials may beused and/or the electrostatic shield 180 can be plated with othermetallic materials. The use of an electrostatic shield reduces thecapacitive coupling, thereby reducing the plasma potential and, hence,permitting independent control of the ion density and the ion energy.The ion density and the ion energy can be independently controlled byadjusting the power to the coil and the power to the substrate bias,respectively. Some capacitive coupling is desired in order to improvethe plasma starting characteristics.

The plasma source assembly 110 depicted in FIG. 2 includes a plenumcooling plate 200, which is detachably mounted to an upper surface ofthe outer shield 150 whereby the gas inject assembly 140 and theelectrostatic shield 180 are secured when the outer shield 150 isattached to the process chamber 120. The plenum cooling plate 200functions as a manifold that circulates cooling fluid, which ispreferably a dielectric fluid, to cool the source resonator cavity 172and the gas inject assembly 140. The plenum cooling plate includesappropriate seals and grounding features. A viewing window 202 islocated between the gas inject assembly 140 and plenum cooling plate200. The window 202 has appropriate vacuum and fluid seals. A window mayor may not be employed. The plenum cooling plate 200 is preferably madefrom aluminum alloy plate stock, however other alternative materials canbe used.

The plenum cooling plate 200 supplies cooling fluid to one or moresupply cooling rods 210 located radially outside the helical coil 190 inthe resonator cavity 172, as depicted in FIGS. 2 and 3. The plenumcooling plate 200 has a supply inlet 204 that receives cool dielectriccooling fluid and transfers the fluid via a supply chamber 205 to thevarious supply cooling rods 210 distributed about the resonator cavity172. The supply cooling rods 210 have holes 212 in sidewalls located sofluid is forced in a circumferential direction inside the resonatorcavity 172, as generally depicted using dashed lines in FIG. 3.

The plenum cooling plate 200 receives cooling fluid from one or morereturn cooling rods 220 located radially inside the helical coil 190 inthe resonator cavity 172, as depicted in FIGS. 2 and 3. Cooling fluid isreturned through the bottom of each tube 220 (depicted with a sectionremoved in FIG. 3), each exiting to a return chamber 207. Chamber 207 isconnected to a return outlet 206 of the plasma cooling plate 200.

Cooling fluid also returns to the return chamber 207 through severalholes or return openings 209 in an uppermost part of the resonatorcavity 172. Air bubbles naturally rise to the highest portions of theresonator cavity 172 as they are circulated by the dielectric coolingfluid. As the bubbles reach the uppermost part of the resonator cavity172, the bubbles proceed through holes 209 connecting the resonatorcavity 172 with the return chamber 207 in the plenum cooling plate 200.Cooling fluid containing the bubbles is then channeled to the gas injectassembly 140 via circulation chambers 208 prior to exiting the plasmasource assembly 110 via the return outlet 206 and returning to a remotefluid cooling assembly, where the bubbles are collected and removed.Higher power settings are possible for plasma generated when air bubblesare removed from the resonator cavity 172, thereby resulting in fasteretching times.

The cooling rods 210, 220 are arranged as depicted in FIGS. 2-5 to lockcoil insulators 240 and insulating spacers 230 securely in place, andhold the helical coil 190 in a predetermined position based on itsfrequency-based tuning. The helical coil 190 extends through the coilinsulators 240, which maintain proper spacing of the helical coil 190.The coil insulators 240 are stacked between insulating spacers 230. Theinsulating spacers 230 maintain proper spacing between the cooling rods210, 220, and maintain the location of the coil insulators 240. Thecooling rods 210, 220, coil insulators 240, and coil spacers 230 arepreferably made of dielectric material such as Teflon, Rexolite, orother similar dielectric or ceramic material.

The gas inject assembly 140 is retained between the plenum cooling plate200 and the dielectric chamber wall 160. Fasteners 142 near a center ofthe gas inject assembly 140 retain the assembly 140 to the plenumcooling plate 200. Other fasteners 142, located on the outer peripheryof the plenum cooling plate 200, attach the plenum cooling plate 200 tothe uppermost plate 156 of the cavity. The fasteners 142 are preferablyremovable by hand, thereby requiring no tools to retain the gas injectassembly 140. Process gas is supplied to a gas plenum area 144, and fromthe gas plenum area 144 the gas is manifolded to a multitude of gasinject holes 146 located on a lower surface of the gas inject assembly140. The gas inject assembly 140 is preferably made from aluminum alloyplate stock, and can be subsequently processed using, for example, ananodization process. Alternatively, the gas inject assembly 140 can beformed using other materials and surface treatments.

FIGS. 2, 3, 4 and 5 depict a helical coil 190. FIGS. 3 through 5 depictcoil insulator geometry and locking features of insulators, spacers andcooling rods. The coil insulators 240 of the spacer 230 interlock withthe cooling rods 210, 220 and space the turns of the helical coil 190 ata correct distance from each other as required by a particular processand design considerations in order to achieve a desired resonancefrequency. An upper end of the coil 190 is affixed to the cavity 172.The method used to attach the upper end of the coil 190 to the resonatorcavity 172 can be mechanical, soldered, or welded, dependant onmaterials used and functional requirements present in the design. In apreferred method, the helical coil 190 is attached to a brass plug usinga low temperature soldering method. Prior to the low temperaturesoldering step, the brass plug is soldered to the resonator cavity 172using a high temperature soldering method. The soldering processdescribed above provides advantageous grounding of the helical coil 190to the resonator cavity 172. At a lower end of coil 190 opposite theupper end, the helical coil is electrically open. At the lower end, thehelical coil 190 is terminated in a rounded tip, which includes a portthrough to an inside of the helical coil 190. Cooling fluid is forcedthrough the inside of the helical coil 190 from the supply inlet via asupply chamber 205 of the plenum cooling plate 200. Fluid exits the coil190 through the tip and mixes with cooling fluid already circulating inthe resonator cavity 172. A tap 196 intersects the helical coil 190 at alocation along the coil 190. The tap 196 is a connection to an externalFast Match Assembly (FMA). The Fast Match Assembly (not shown) comprisesan impedance match network for matching the output impedance of a RFgenerator (not shown) to the input impedance of the plasma source andplasma. The FMA incorporates automatic control hardware and software foradjusting the impedance match according to changes in the load (plasma)impedance. Impedance match network design and the control thereof forplasma processing operations are well known to those skilled in the artof plasma source design and RF (radio frequency) electronics.Appropriate insulators and seals are positioned as required tofacilitate the connection of the tap to the FMA at interface 241. Thehelical coil 190 is preferably made from copper tubing, howeveralternative materials can be utilized. The helical coil 190 may or maynot be plated with some other metallic material. For example, asdescribed above, helical coil 190, configured to have a grounded end, anopen end opposite the grounded end and a tap location between the openend and the grounded end, can be designed as a quarter wave or half waveresonator. Helical resonators are well known to those of skill in theart of plasma source design. In an alternate embodiment, coil 190comprises a tap location at a first end of coil 190 and a grounded endat a second end of coil 190.

The dielectric chamber wall or process tube 160 is installed in theassembly as depicted in FIG. 2. Appropriate seals 162, 166, 173, 174 andload bearing spacers 164, 168, 171 are utilized to secure the processtube 160 in a correct position. The seals 162, 166, 173, 174 and loadbearing spacers 164, 168, 171 can be configured as described in U.S.Application Ser. No. 60/256,330, which is incorporated herein byreference, or can be positioned as separate parts as depicted in FIG. 2.The outer rim of the process tube 160 has at least one dielectric pin169 installed on the outer surface, protruding through the outer shieldor housing 150. The dielectric pin(s) 169 retain the process tube 160 inposition as the plasma source is rotated on hinges from the processchamber 120 opening during maintenance events. The dielectric pin(s) 169are made from Teflon or other dielectric material and are removed, byhand, to facilitate removal of the dielectric chamber wall 160 whenmaintenance is necessary. The absence of mechanical fasteners or otherparts other than dielectric pins allows for very fast removal andreplacement of the dielectric chamber wall 160 when process requirementsdeem a maintenance event necessary.

It should be noted that the exemplary embodiments depicted and describedherein set forth the preferred embodiments of the present invention, andare not meant to limit the scope of the claims hereto in any way.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A plasma processing system comprising: a process chamber; a chuckassembly provided within said process chamber; a gas inject assemblyprovided opposite said chuck assembly; and a plasma source assemblycomprising a dielectric chamber wall, a helical coil, and an outershield mounting said gas inject assembly to said process chamber, saidouter shield comprising a plurality of plates.
 2. The plasma processingsystem according to claim 1, further comprising at least one sealingmember provided between adjacent plates of said plurality of plates. 3.The plasma processing system according to claim 1, further comprisingmeans for stacking and detachably joining said plurality of plates. 4.The plasma processing system according to claim 1, further comprising:said dielectric chamber wall and said plurality of plates defining aresonator cavity; and a helical coil provided within said resonatorcavity.
 5. The plasma processing system according to claim 1, furthercomprising means for tuning said helical coil to a predeterminedfrequency.
 6. The plasma processing system according to claim 4, furthercomprising: means for circulating cooling fluid throughout the plasmaprocessing system; and a plenum cooling plate defining a manifoldconfigured to supply cooling fluid to said means for circulating.
 7. Theplasma processing system according to claim 6, wherein said gas injectassembly is provided between said dielectric chamber wall and saidplenum cooling plate.
 8. The plasma processing system according to claim6, further comprising means for removing bubbles from the cooling fluid.9. The plasma processing system according to claim 6, wherein saidplenum cooling plate is configured to supply cooling fluid to a firstcooling rod provided within said resonator cavity.
 10. The plasmaprocessing system according to claim 9, wherein: said first cooling rodis provided radially outside said helical coil; and said first coolingrod has at least one outlet hole configured to discharge the coolingfluid in a circumferential direction within said resonator cavity. 11.The plasma processing system according to claim 9, wherein: said plenumcooling plate is configured to receive cooling fluid from a secondcooling rod provided within said resonator cavity; said second coolingrod is provided radially inside said helical coil; and said secondcooling rod has at least one inlet hole configured to receive thecooling fluid from within said resonator cavity.
 12. The plasmaprocessing system according to claim 11, further comprising: a spacerprovided between said first cooling rod and said second cooling rod; andcoil insulators having holes configured to receive said helical coil.